1. Field of the Invention
The present invention is related to a network transmission method and a network transmission system, and more particularly, a network transmission method and a network transmission system used for a multi-layer network address translator structure.
2. Description of the Prior Art
With the development of network technology, peer-to-peer connections have been widely used. By using peer-to-peer connections, multiple nodes can be connected to one another for exchanging data without a relay server. However, when nodes are located under a structure of multi-layer network address translator, it is difficult to build a peer-to-peer connection between two nodes. FIG. 1 illustrates that a peer-to-peer connection fails to be built under a multi-layer network address translator structure according to a prior art. A network node 112 and a network address translator 130 are located under a network address translator 120, and a network node 111 is located under the network address translator 130. When the server 110 tries to arrange a peer-to-peer connection between the nodes 111 and 112, it will fail to connect the two nodes 111 and 112 (through the path Pt1) by using the external addresses and the external port numbers of the two nodes 111 and 112 corresponding to the network address translator 120 because of the hairpinning limitation defined in the document RFC 5128 issued by Internet Engineering Task Force (IETF). It will also fail to build the peer-to-peer connection between the two nodes 111 and 112 by using the internal addresses and internal port numbers of the nodes 111 and 112. The reason is, since the two nodes are not of a same layer of the hierarchy of the multi-layer network address translator structure, when the node 112 sends a packet toward the internal address and the internal port number of the node 111, the packet cannot be sent to the node 111 though the network address translator 130 (as the path Pt2). Hence, a solution is required for resolving the abovementioned problem of failing to build a peer-to-peer connection in the field.